Process for producing aviation fuel base oil

ABSTRACT

The present invention provides a process of producing an aviation fuel base oil having excellent combustibility, oxidation stability and life cycle characteristics, hydrotreating in the presence of hydrogen a feedstock comprising an oxygen-containing hydrocarbon compound originating from an animal or vegetable fat (preferably an animal or vegetable fat that contains fatty acids each having 10 to 14 carbon atoms in the fatty acid carbon chain in the total amount of 60 percent by mass or more) and a sulfur-containing hydrocarbon compound. The present invention also provides a process for producing an aviation fuel base oil by blending such an aviation fuel base oil and an aviation fuel base oil produced by refining crude oil.

TECHNICAL FIELD

The present invention relates to a process for producing an aviationfuel base oil.

BACKGROUND ART

Attention has been focused on the effective use of biomass energies inorder to prevent global warming. In particular, those originating fromvegetables in particular can make effectively the use of hydrocarbonsconverted from carbon dioxide by photosynthesis through the growthprocess of the vegetables and thus have a nature so-called carbonneutral, which does not lead to an increase in carbon dioxide in theatmosphere in view of the life cycle. Biomass fuel has had a high degreeof expectation as an alternative energy to petroleum from the viewpointof depletion of petroleum resources and inflating oil prices.

The use of biomass energy has been variously studied also in the fieldof fuels for transportation. For example, if a fuel originating from ananimal or vegetable oil can be used as diesel fuel, the fuel is expectedto take an effective role in carbon dioxide emission reduction becauseof its synergistic effect with the high energy efficiency of a dieselengine. Examples of generally known diesel fuels using animal orvegetable oils includes fatty acid methyl ester oils (abbreviated as“FAME”). The FAME is produced by ester-exchanging triglyceride, which isa general structure of an animal or vegetable oil, with methanol withthe aid of the action of an alkali catalyst. Various studies have alsobeen carried out so as to use the FAME not only for diesel fuel but alsofor aviation fuel, i.e., jet fuel. Aircrafts spent enormous amounts offuel and have been affected largely by the recent inflating oil prices.Under these circumstances, much attention has been paid to biomass fuelas an important item taking a role not only as a measure for preventingglobal warming but also as fuel alternative to petroleum. Currently, theuse of the FAME in the form of a mixture with a petroleum-based jet fuelhas been carried out in some airline companies although on a trialbasis.

However, it is necessary to dispose of glycerin produced as a by-productduring the process of producing the FAME as described in PatentLiterature 1 below. Costs and energies are also required to clean theresulting oil.

Furthermore, the FAME has concerns about its low temperatureperformances and oxidation stability. Since aviation fuels in particularare exposed to extremely low temperatures during flight at highaltitudes, they are required to satisfy highly strict low temperatureperformance standards. When the FAME is to be used, it is very much asituation that the FAME must be blended with petroleum-based jet fueland the amount of the FAME must be small. For oxidation stability, thespecification of aviation fuel has established the addition ofantioxidants. However, when consideration is given to the stability ofthe base oil, the amount thereof must be small as well as for lowtemperature performance.

Citation List Patent Literatures

Patent Literature 1: Japanese Patent

Application Laid-Open Publication No. 2005-154647

SUMMARY OF INVENTION Technical Problem

The present invention intends to solve the foregoing problems and has anobject to provide a process for producing an aviation fuel base oilhaving excellent combustibility, oxidation stability and life cyclecharacteristics.

Solution to Problem

The present invention has been accomplished on the basis of the resultsof extensive studies carried out the inventors to solve the aboveproblems.

That is, the present invention relates to a process for producing anaviation fuel base oil comprising hydrotreating in the presence ofhydrogen a feedstock comprising an oxygen-containing hydrocarboncompound originating from an animal or vegetable fat and asulfur-containing hydrocarbon compound.

The present invention also relates to the foregoing process, wherein thefeedstock further comprises a petroleum base oil produced by refiningcrude oil

The present invention also relates to any of the forgoing processes,wherein the total of the compositions of the fatty acids having a fattyacid hydrocarbon chain of 10 to 14 carbon atoms in the animal orvegetable fat is 60 percent by mass or more.

The present invention also relates to any of the foregoing processes,wherein the hydrotreating comprises a step wherein said feedstock ishydrotreated in the presence of hydrogen using a catalyst a catalystcomprising a porous inorganic oxide comprising two or more types ofelements selected from aluminum, silicon, zirconium, boron, titanium andmagnesium and one or more types of metals selected from the groupconsisting of the Groups 6A and 8 elements of the periodic table,supported thereon, under conditions where the hydrogen pressure is from2 to 13 MPa, the liquid hourly space velocity is from 0.1 to 3.0 h⁻¹,the hydrogen/oil ratio is from 150 to 1500 NL/L, and the reactiontemperature is from 150 to 480° C.

The present invention also relates to any of the foregoing processes,wherein the hydrotreating comprises a step wherein the hydrotreated oilproduced in the said hydrotreating step of claim 4 is further isomerizedin the presence of hydrogen using a catalyst comprising a porousinorganic oxide comprising two or more types of elements selected fromaluminum, silicon, zirconium, boron, titanium, magnesium and zeolite andone or more types of metals selected from the group consisting of theGroup 8 elements of the periodic table, supported thereon, underconditions where the hydrogen pressure is from 2 to 13 MPa, the liquidhourly space velocity is from 0.1 to 3.0 h⁻¹, the hydrogen/oil ratio isfrom 250 to 1500 NL/L, and the reaction temperature is from 150 to 380°C.

The present invention also relates to a process for producing anaviation fuel base oil wherein the aviation fuel base oil is produced byblending an aviation fuel base oil produced by any of the foregoingprocesses and an aviation fuel base oil produced by refining crude oil.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention provides a process for producing an environmentfriendly aviation fuel base oil having excellent combustibility,oxidation stability and lifecycle characteristics resulting from itscarbon neutral characteristics and can contribute to primary energydiversification.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below.

In the present invention, there is used a feedstock comprising anoxygen-containing hydrocarbon compound originating from an animal orvegetable fat and a sulfur-containing hydrocarbon compound.

Examples of the animal or vegetable fat include beef tallow, rapeseedoil, soy bean oil, and palm oil. Any fat may be used as the animal orvegetable fat in the present invention. Alternatively, waste oilsresulting from the use of these fats may be used. However, in view ofcarbon neutral, it is preferable to use vegetable fats. In view of theyield of kerosene fraction after hydrotreating, it is preferable to usevegetable fats wherein the total of structural ratio (fatty acidcomposition) of fatty acid groups each having a fatty acid carbon chainof 10 to 14 is 60 percent by mass or more. Preferable vegetable fatsthat can be thought from this view point are coconut oil and palm oil.These fats may be used alone or in combination.

The fatty acid composition is a value determined in accordance withStandard Test Method of Analysis of Oils and Fats (established by JapanOil Chemists' Society) (1993) “2.4.21.3-77 Fatty Acid Composition (FIDProgrammed Temperature Gas Chromatograph Method)” using a programmedtemperature gas chromatograph equipped with a flame ionization detector(FID) from methyl ester prepared in accordance with Standard Test Methodof Analysis of Oils and Fats (established by Japan Oil Chemists'Society) (1991) “2.4.20.2-91 Method for Preparing Fatty Acid MethylEster (Boron Trifluoride-Methanol Method)”, and refers to a constitutiveratio (mass %) of each fatty acid group constituting the fat.

In general, an oxygen-containing hydrocarbon compound originating froman animal or vegetable fat is a compound having a fatty acidtriglyceride structure but may contain other fatty acids oroxygen-containing hydrocarbon compounds modified to ester bodies, suchas fatty acid methyl ester. However, the vegetable fat preferablycontains mainly a component having a triglyceride structure with theobjective of reducing carbon dioxide emissions because carbon dioxide isgenerated upon production of fatty acids or fatty acid esters fromvegetable fats. In the present invention, the ratio of the compoundhaving a triglyceride structure in the oxygen-containing hydrocarboncompound contained in the feedstock is preferably 90 percent by mole ormore, more preferably 92 percent by mole or more, more preferably 95percent by mole or more.

Alternatively, the feedstock may further contain a petroleum-based baseoil produced by refining crude oil. Examples of the petroleum-based baseoil produced by refining crude oil include fractions produced byatmospheric or vacuum distilling crude oil and fractions producedthrough reactions such as hydrodesulfurizatin, hydrocracking, fluidcatalytic cracking, and catalytic reforming. The amount of thesefractions may be arbitrarily set as long as the sulfur content of thefeedstock is within the predetermined range described below.Furthermore, the petroleum-based base oil produced by refining crude oilmay be a compound originating from chemical products or a synthetic oilproduced through a Fischer-Tropsch reaction.

No particular limitation is imposed on the content ratio of thepetroleum-based base oil produced by refining crude oil, in thefeedstock. However, the ratio is preferably from 20 to 70 percent byvolume, more preferably from 30 to 60 percent by volume.

No particular limitation is imposed on the sulfur-containing hydrocarboncompound also contained in the feedstock. However, specific examplesinclude sulfide, disulfide, polysulfide, thiol, thiophene,benzothiophene, dibenzothiophene, and derivatives thereof. Thesulfur-containing hydrocarbon compound contained in the feedstock may bea single compound or a mixture of two or more types of these compounds.Alternatively, a petroleum hydrocarbon fraction containing sulfur may beused as the sulfur-containing hydrocarbon compound.

The sulfur content of the feedstock is preferably 1 to 50 ppm by mass,more preferably 5 to 30 ppm by mass, more preferably 10 to 20 ppm bymass in terms of sulfur on the basis of the total mass of the feedstock.If the sulfur content in terms of sulfur is less than 1 ppm by mass, ittends to be difficult to maintain stable deoxidization activity. If thesulfur content is in excess of 50 ppm by mass, the sulfur concentrationof the light gas exhausted during hydrorefining process will beincreased. Furthermore, the hydrorefined oil is likely to be increasedin sulfur content and thus would adversely affect the exhaust gaspurification device of a diesel engine when it is used therefor. Thesulfur content used herein denotes the mass content of sulfur measuredin accordance with JIS K 2541 “Determination of sulfur content” or themethod described in ASTM-5453.

The sulfur-containing hydrocarbon compound contained in the feedstockmay be mixed with the oxygen-containing hydrocarbon compound originatingfrom an animal or vegetable fat beforehand and then introduced into areactor of a hydrotreating unit or alternatively may be supplied to asection upstream the reactor when the oxygen-containing hydrocarboncompound originating from an animal or vegetable is introduced therein.

The aviation fuel base oil of the present invention may be prepared byhydrotreating the above-described feedstock.

Preferably, hydrotreating contains the following hydrotreating steps. Inthe present invention, hydrotreating is carried out preferably underconditions where the hydrogen pressure is in the range of 2 to 13 MPa,the liquid hourly space velocity (LHSV) is in the range of 0.1 to 3.0h⁻¹ and the hydrogen/oil ratio is in the range of 150 to 1500 NL/L, morepreferably under conditions where the hydrogen pressure is in the rangeof 2 to 13 MPa, the liquid hourly space velocity is in the range of 0.1to 3.0 h⁻¹, and the hydrogen/oil ratio is in the range of 150 to 1500NL/L, more preferably under conditions where the hydrogen pressure is inthe range of 3 to 10.5 MPa, the liquid hourly space velocity is in therange of 0.25 to 1.0 h⁻¹, and the hydrogen/oil ratio is in the range of300 to 1000 NL/l.

Each of the conditions is a factor exerting an influence on the reactionactivity. For example, if the hydrogen pressure and hydrogen/oil ratioare less than the lower limits, the reactivity tends to reduce, and theactivity tends to reduce rapidly. If the hydrogen pressure andhydrogen/oil ratio exceed the upper limits, an enormous plant investmentfor a compressor may be required. Lower liquid hourly space velocitytends to be more advantageous for the reactions. However, if the liquidhourly space velocity is lower than the lower limit, an enormous plantinvestment for construction of a reactor with an extremely large volumemay be required. If the liquid hourly space velocity exceeds the upperlimit, the reaction tends to proceed insufficiently.

The reaction temperature can be arbitrarily adjusted so as to obtain theintended decomposition rate of the heavy fraction of the feedstock orthe intended fraction yield. The average temperature in the wholereactor is set to generally from 150 to 480° C., preferably from 200 to400° C., more preferably from 260 to 360° C. If the reaction temperatureis lower than 150° C., the reaction would not proceed sufficiently. Ifthe reaction temperature exceeds 480° C., excessive decomposition wouldproceed and the yield of the liquid product would be reduced.

The catalyst for hydrotreating is a catalyst comprising a porousinorganic oxide comprising two or more types of elements selected fromaluminum, silicon, zirconium, boron, titanium and magnesium and one ormore types of metals selected from the group consisting of the Groups 6Aand 8 elements of the periodic table, supported thereon.

The support of the hydrotreating catalyst is a porous inorganic oxidecontaining two or more elements selected from aluminum, silicon,zirconium, boron, titanium and magnesium. The support is generally analumina-containing porous inorganic oxide. Examples of other componentsconstituting the support include silica, titania, zirconia, boria andmagnesia. The support is preferably a composite oxide containing aluminaand at least one or more components selected from the other constitutingcomponents. The support may further contain phosphorus in addition tothese components. The total content of the components other than aluminais preferably from 1 to 20 percent by mass, more preferably 2 to 15percent by mass. If the total content is less than 1 percent by mass,the resulting catalyst fails to obtain a sufficient catalytic surfacearea and thus would be reduced in activity. If the total content is morethan 20 percent by mass, the acidic properties of the support areincreased, possibly leading to a reduction in activity caused by theformation of coke. When phosphorus is contained as a supportconstituting component, the content of phosphorus is from 1 to 5 percentby mass, more preferably from 2 to 3.5 percent by mass in terms ofoxide.

No particular limitation is imposed on the raw materials that areprecursors of silica, titania, zirconia, boria and magnesia that are thesupport constituting components other than alumina. Therefore, asolution containing silicon, titanium, zirconium, boron or magnesium isgenerally used. For silicon, silicic acid, sodium silicate, and silicasol may be used. For titanium, titanium sulfate, titanium tetrachloride,and various alkoxide salts may be used. For zirconium, zirconium sulfateand various alkoxide salts may be used. For boron, boric acid may beused. For magnesium, magnesium nitrate may be used. For phosphorus,phosphoric acid and alkali metal salts thereof may be used.

The raw materials of these support constituting components other thanalumina are preferably added at any stage prior to calcination of thesupport. For example, the raw materials may be added to an aluminumaqueous solution which is then formed into an aluminum hydroxide gelcontaining these support constituting components, or may be added to aprepared aluminum hydroxide gel. Alternatively, the raw materials may beadded at a step of kneading a mixture of water or an acid aqueoussolution and a commercially available alumina intermediate or boehmitepowder. Preferably, these support constituting components are containedin an aluminum hydroxide gel during the process of preparation thereof.Although the mechanism exhibiting advantageous effects attained byaddition of these support constituting components other than alumina hasnot been elucidated, it is assumed that these components form a complexoxide state together with aluminum. It is thus presumed that thisincrease the surface area of the support and cause some interaction withthe active metals, thereby giving influences to the activity of thecatalyst.

The catalyst for hydrotreating contains at least one metal, preferablytwo or more metals selected from the Groups 6A and 8 metals of theperiodic table, as an active metal. Examples of such metals includeCo—Mo, Ni—Mo, Ni—Co—MO, and Ni—W. Upon hydrotreating, these metals areconverted to be in the form of sulfides before being used.

The total supported amount of the active metals, for example, W and Mois preferably from 12 to 35 percent by mass, more preferably from 15 to30 percent by mass, in terms of oxide, of the catalyst mass. If theamount is less than 12 percent by mass, the catalytic activity would bereduced because the number of active sites is reduced. If the amount ismore than the upper limit, the metals fail to disperse effectively,possibly leading to a reduction in catalytic activity. The totalsupported amount of Co and Ni is preferably from 1.5 to 10 percent bymass, more preferably from 2 to 8 percent by mass, in terms of oxide, ofthe catalyst mass. If the amount is less than 1.5 percent by mass, asufficient co-catalytic effect can not be attained, possibly leading toa reduction in catalytic activity. If the amount is more than 10 percentby mass, the metals fail to disperse effectively, possibly leading to areduction in catalytic activity.

No particular limitation is imposed on the method of supporting theactive metals on any of the above-described hydrotreating catalysts.Therefore, any conventional method for producing a usual desulfurizationcatalyst may be employed. A method is preferably employed in which asupport is impregnated with a solution containing salts of the activemetals. Alternatively, an equilibrium adsorption method, pore-fillingmethod, or incipient-wetness method is also preferably used. Forexample, the pore-filling method is a method in which the pore volume ofa support is measured in advance, and then the support is impregnatedwith the same volume of a metal salt solution. There is no particularrestriction on the method of impregnating the support with a solution.Therefore, any suitable method may be used depending on the amount ofthe metals to be supported and physical properties of the support.

The reactor for hydrotreating may be of a fixed bed mode. That is,supply of hydrogen to the feedstock may be carried out in the form ofcounter flow or parallel flow. Alternatively, counter flow and parallelflow may be combined in a plurality of reactors. The supply mode of thefeedstock is generally down flow. Gas-liquid cocurrent flow may beemployed. Furthermore, a single reactor is used alone or a plurality ofreactors may be used in combination. A single reactor with the interiorsegmented into a plurality of catalyst beds may also be employed. In thepresent invention, the hydrotreated oil resulting from hydrotreatment inthe reactor is fractionated into predetermined fractions throughgas-liquid separation and rectification. A gas-liquid separation deviceor any other by-produced gas removal device may be installed between theplurality of reactors or in the product recovering step in order toremove water generated in associated with the reaction and by-producedgas such as carbon monoxide, carbon dioxide, and hydrogen sulfide.Examples of the by-produced gas removal device include high pressureseparators and the like.

Hydrogen gas is generally introduced into a first reactor via its inlet,accompanying the feedstock, before or after the feedstock passes througha heating furnace. Alternatively, hydrogen gas may be introduced fromthe spaces between the catalyst beds or between a plurality of reactorsfor the purposes of controlling the temperature in the reactors andmaintaining the hydrogen pressure over the whole reactors as much aspossible. Hydrogen to be introduced in such a manner is referred to as“quenching hydrogen”. The ratio of the quenching hydrogen to thehydrogen introduced, accompanying the feedstock is preferably from 10 to60 percent by volume, more preferably from 15 to 50 percent by volume.The ratio of less than 10 percent by volume would cause a tendency thatthe reaction at reaction sites in the subsequent stages does not proceedsufficiently. The ratio in excess of 60 percent by volume would cause atendency that the reaction near the inlet of the reactor does notproceed sufficiently.

In the process of producing the aviation fuel base oil of the presentinvention, a specific amount of a recycled oil may be incorporated inthe feedstock to reduce the amount of heat generated in thehydrotreating reactor upon hydrotreating of the feedstock. The amount ofthe recycled oil is from 0.5 to 5 times by mass of the oxygen-containinghydrocarbon compound originating from an animal or vegetable fat and maybe adjusted appropriately within this range depending on the maximumoperation temperature in the hydrotreating reactor. This is because onassumption that the specific heats of both the recycled oil and theoxygen-containing hydrocarbon compound are the same, the temperatureincrease upon they are mixed at 1:1 is half of that of the case whereonly substances originating from animal or vegetable fats are reacted,and thus the reaction temperature can be sufficiently lowered if theamount of the recycled oil is within the above range. The recycled oilin excess of 5 times by mass of the oxygen-containing compound wouldreduce the concentration thereof, resulting in a reduction in reactivityand would increase the flow rate in piping, resulting in an increase inload. When the content of the recycled oil is less than 0.5 times bymass of the oxygen-containing compound, a rise in temperature can not besuppressed sufficiently.

No particular limitation is imposed on the method of mixing thefeedstock and the recycled oil. For example, they are mixed in advanceand introduced into a reactor of a hydrotreating unit. Alternatively,the recycled oil may be introduced at a prior stage of the reactor whenthe feedstock is introduced thereinto. Further alternatively, they maybe introduced into the spaced between a plurality of reactors connectedin series or between the catalyst layers formed by dividing the catalystlayer in a single reactor.

Preferably, the recycled oil contains a portion of a hydrotreated oilproduced by hydrotreating the feedstock and then removing by-productssuch as water, carbon monoxide, carbon dioxide, and hydrogen sulfide.Furthermore, the recycled oil preferably contains a portion of a productproduced by isomerizing each of a light fraction, a middle fraction, anda heavy fraction, fractionated from the hydrotreated oil or a portion ofa middle fraction fractionated from a product produced by isomerizingthe hydrotreated oil.

The hydrotreating used in the present invention may further contain astep of isomerizing the hydrotreated oil produced through theabove-described hydrotreating step.

The sulfur content of the hydrotreated oil that is a feedstock ofisomerization is preferably 1 ppm by mass or less, more preferably 0.5ppm by mass. A sulfur content of greater than 1 ppm by mass wouldpossibly prevent the progress of hdyroisomerization. Additionally, forthe same reason, the sulfur content of a reaction gas containinghydrogen to be introduced together with the hydrotreated oil isnecessarily low sufficiently and preferably 1 ppm by volume or less,more preferably 0.5 ppm by volume or less.

The isomerization treatment is carried out in the presence of hydrogenpreferably under conditions where the hydrogen pressure is from 2 to 13MPa, the liquid hourly space velocity is from 0.1 to 3.0 h⁻¹, and thehydrogen/oil ratio is from 250 to 1500 NL/L, more preferably underconditions where the hydrogen pressure is from 2.5 to 10 MPa, the liquidhourly space velocity is from 0.5 to 2.0 h⁻¹, and the hydrogen/oil ratiois from 380 to 1200 NL/L, more preferably under conditions where thehydrogen pressure is from 3 to 8 MPa, the liquid hourly space velocityis from 0.8 to 1.8 h⁻¹, and the hydrogen/oil ratio is from 350 to 1000NL/L.

Each of the conditions is a factor exerting an influence on the reactionactivity. For example, if the hydrogen pressure and hydrogen/oil ratioare less than the lower limits, the reactivity tends to reduce, and theactivity tends to reduce rapidly. If the hydrogen pressure andhydrogen/oil ratio exceed the upper limits, an enormous plant investmentfor a compressor may be required. Lower liquid hourly space velocitytends to be more advantageous for the reactions. However, if the liquidhourly space velocity is lower than the lower limit, an enormous plantinvestment for construction of a reactor with an extremely large volumemay be required. If the liquid hourly space velocity exceeds the upperlimit, the reaction tends to proceed insufficiently.

The reaction temperature can be arbitrarily adjusted so as to obtain theintended decomposition rate of the heavy fraction of the feedstock orthe intended fraction yield. The reaction temperature is preferably from150 to 380° C., more preferably from 240 to 380° C., more preferablyfrom 250 to 365° C. If the reaction temperature is lower than 150° C.,the reaction would not proceed sufficiently. If the reaction temperatureexceeds 380° C., excessive cracking or other side reactions wouldproceed, possibly resulting in a reduction in the liquid product yield.

The catalyst for isomerization is a catalyst comprising a porousinorganic oxide comprising a substance selected from aluminum, silicon,zirconium, boron, titanium, magnesium, and zeolite and one or more typesof metals selected from the group consisting of the Group 8 elements ofthe periodic table, supported thereon.

Examples of the porous inorganic oxide used as the support of thecatalyst for isomerization include alumina, titania, zirconia, boria,silica, and zeolite. In the present invention, the support is preferablycomposed of alumina and at least one type selected from titania,zirconia, boria, silica, and zeolite. No particular limitation isimposed on the method of producing the support. Therefore, there may beemployed any method using raw materials in the form of sols or saltcompounds each containing any of the elements. Alternatively, thesupport may be prepared by forming a complex oxide or hydroxide such assilica alumina, silica zirconia, alumina titania, silica titania, andalumina boria and then adding at any step alumina in the form of aluminagel, a hydroxide, or a suitable solution. Alumina can be contained inany percentage to other oxides on the basis of the porous support.However, the content of alumina is preferably 90 percent by mass orless, more preferably 60 percent by mass or less, more preferably 40percent by mass or less, and preferably 10 percent by mass or more, morepreferably 20 percent by mass or more, of the support mass.

Zeolite is a crystalline alumino silicate. Examples of the crystallinestructure include faujasite, pentasil, and mordenite. These zeolites maybe those ultra-stabilized by a specific hydrothermal treatment and/oracid treatment or those whose alumina content is adjusted. Preferredzeolites are those of faujasite and mordenite types, and particularlypreferred zeolites are those of Y and beta types. The zeolites of Y typeare preferably ultra-stabilized. The ultra-stabilized zeolite have amicro porous structure peculiar thereto, so-called micro pores of 20 Åor smaller and also newly formed pores in the range of 20 to 100 Å. Thehydrothermal treatment may be carried out under known conditions.

The active metal of the catalyst for isomerization is one or more metalsselected from the group consisting of the Group 8 elements of theperiodic table. Among these metals, the active metal is preferably oneor more metals selected from Pd, Pt, Rh, Ir, Au, and Ni and morepreferably a combination thereof. Preferable combinations include Pd—Pt,Pd—Ir, Pd—Rh, Pd—Au, Pd—Ni, Pt—Rh, Pt—Ir, Pt—Au, Pt—Ni, Rh—Ir, Rh—Au,Rh—Ni, Ir—Au, Ir—Ni, Au—Ni, Pd—Pt—Rh, Pd—Pt—Ir, and Pt—Pd—Ni. Morepreferable combinations include Pd—Pt, Pd—Ni, Pt—Ni, Pd—Ir, Pt—Rh,Pt—Ir, Rh—Ir, Pd—Pt—Rh, Pd—Pt—Ni, and Pd—Pt—Ir. Further more preferableexamples include Pd—Pt, Pd—Ni, Pt—Ni, Pd—Ir, Pt—Ir, Pd—Pt—Ni, andPd—Pt—Ir.

The content of the active metal(s) is preferably from 0.1 to 2 percentby mass, more preferably from 0.2 to 1.5 percent by mass, morepreferably from 0.5 to 1.3 percent by mass in terms of metal on thebasis of the catalyst mass. If the total content is less than 0.1percent by mass, the catalytic activity would be reduced because thenumber of active sites is reduced. If the total content is more than 2percent by mass, the metals fail to disperse effectively, possiblyresulting in an insufficient catalytic activity.

No particular limitation is imposed on the method of supporting theactive metals on any of the catalysts for isomerization. Therefore, anyconventional method for producing a usual desulfurization catalyst maybe employed. A method is preferably employed in which a support isimpregnated with a solution containing salts of the active metals.Alternatively, an equilibrium adsorption method, pore-filling method, orincipient-wetness method is also preferably used. For example, thepore-filling method is a method in which the pore volume of a support ismeasured in advance, and then the support is impregnated with the samevolume of a metal salt solution. No particular limitation is imposed onthe method of impregnating the support with a solution. Therefore, anysuitable method may be used depending on the amount of the metals to besupported and physical properties of the support.

The isomerization catalyst used in the present invention is preferablyused after the active metal(s) contained therein has been subjected to areduction treatment before put in use in the reaction. No particularlimitation is imposed on the conditions for the reduction treatment.However, the active metal(s) are reduced by being subjected to atreatment at a temperature of 200 to 400° C., preferably 240 to 380° C.under hydrogen current. It the reduction temperature is lower than 200°C., reduction of the active metal(s) may not proceed sufficiently, andthus the resulting catalyst may not exhibit hydrodeoxidization orhydroisomerization activity. If the reduction temperature is higher than400° C., agglomeration of the active metal(s) proceeds and thussimilarly the resulting catalyst may not exhibit the activities.

The reactor for isomerization may be of a fixed bed mode. That is,supply of hydrogen to the feedstock may be carried out in the form ofcounter flow or parallel flow. Alternatively, counter flow and parallelflow may be combined in a plurality of reactors. The supply mode of thefeedstock is generally down flow. Gas-liquid cocurrent flow may beemployed. Furthermore, a single reactor is used alone or a plurality ofreactors may be used in combination. A single reactor with the interiorsegmented into a plurality of catalyst beds may also be employed.

Hydrogen gas is generally introduced into a first reactor via its inlet,accompanying the feedstock, before or after the feedstock passes througha heating furnace. Alternatively, hydrogen gas may be introduced fromthe spaces between the catalyst beds or between a plurality of reactorsfor the purposes of controlling the temperature in the reactors andmaintaining the hydrogen pressure over the whole reactors. Hydrogen tobe introduced in such a manner is referred to as “quenching hydrogen”.The ratio of the quenching hydrogen to the hydrogen introduced,accompanying the feedstock is preferably from 10 to 60 percent byvolume, more preferably from 15 to 50 percent by volume. The ratio ofless than 10 percent by volume would cause a tendency that the reactionat reaction sites in the subsequent stages does not proceedsufficiently. The ratio in excess of 60 percent by volume would cause atendency that the reaction near the inlet of the reactor does notproceed sufficiently.

If necessary, the isomerized oil resulting from the isomerization may befractionated into a plurality of fractions in a rectification tower. Forexample, the isomerized oil may be fractionated into a light fractionsuch as gas and naphtha fraction, a middle fraction such as kerosene andgas oil fractions, and a heavy fraction such as residues. In this case,the cut temperature between the light fraction and the middle fractionis preferably from 100 to 200° C., more preferably from 120 to 180 o200° C., more preferably from 120 to 160° C., more preferably from 130to 150° C. The cut temperature between the middle fraction and the heavyfraction is preferably from 250 to 360° C., more preferably from 250 to320° C., more preferably from 250 to 300° C., more preferably from 250to 280° C. Such a light hydrocarbon fraction thus generated may bepartially reformed in a steam reforming unit thereby producing hydrogen.Hydrogen thus produced has carbon neutral characteristics and thus canreduce environment load because the feedstock used in the steamreforming is a biomass-originating hydrocarbon. The middle fractionproduced by fractionating the isomerized oil can be suitably used as anaviation fuel base oil.

The aviation fuel base oil of the present invention may be used alone asan aviation fuel but may be mixed with an aviation fuel base oilproduced by refining crude oil in the form of an aviation fuelcomposition. Examples of the aviation fuel base oil produced by refiningcrude oil include aviation fuel fractions produced through a generalpetroleum refining process and a synthetic fuel base oil producedthrough a Fischer-Tropsch reaction or the like using synthetic gascomposed of hydrogen and carbon monoxide. This synthetic fuel base oilis characterized in that does not contain almost no aromatic butcontains a saturated hydrocarbon as the main component and has a highsmoke point. No particular limitation is imposed on the method ofproducing the synthetic gas. Any conventional method may be used.

EXAMPLES

The present invention will be described in more details with referenceto the following examples but is not limited thereto.

(Preparation of Catalyst)

<Catalyst A>

To 3000 g of a 5 mass % sodium aluminate aqueous solution was added 18.0g of sodium silicate No. 3. The resulting mixture was placed into avessel kept at a temperature of 65° C. Separately to this, in anothervessel kept at a temperature of 65° C., a solution was prepared byadding 6.0 g of phosphoric acid (85% concentration) to 3000 g of a 2.5mass % aluminum sulfate aqueous solution. To the solution was addeddropwise the aqueous solution containing sodium aluminate producedabove. The dropwise addition was terminated when the pH of the mixedsolution reached 7.0. The resulting slurry product was passed through afilter thereby producing a cake-like slurry.

The resulting cake-like slurry was transferred to a vessel equipped witha reflux condenser, and 150 ml of distilled water and 10 g of a 27%ammonia aqueous solution were added thereto, followed by heating andstirring at a temperature of 75° C. for 20 hours. The resulting slurrywas placed in a kneader and kneaded while being heated to a temperatureof 80° C. or higher to remove moisture thereby producing a clay-likekneaded product. The resulting kneaded product was extruded into acylinder shape having a diameter of 1.5 mm through an extruder, dried ata temperature of 110° C. for one hour and then calcined at a temperatureof 550° C. thereby producing a molded support.

Into an eggplant-type flask was placed 50 g of the resulting moldedsupport, and also poured an impregnation solution containing 17.3 g ofmolybdenum trioxide, 13.2 g of nickel (II) nitrate hexahydrate, 3.9 g ofphosphoric acid (85% concentration), and 4.0 g of malic acid whiledeaerating with a rotary evaporator. After dried at a temperature of120° C. for one hour, the impregnated sample was calcined at atemperature of 550° C. thereby producing Catalyst A. The physicalproperties of Catalyst A are set forth in Table 1 below.

<Catalyst B>

Into an eggplant-type flask was placed 50 g of a commercially availablesilica alumina support (N632HN manufactured by JGC C&C), and then pouredan aqueous solution of tetraammineplatinum (II) chloride whiledeaerating with a rotary evaporator. The impregnated sample was dried ata temperature of 110° C. and then calcined at a temperature of 350° C.thereby producing Catalyst B. The amount of platinum supported onCatalyst B was 0.5 percent by mass on the basis of the total mass of thecatalyst. The physical properties of Catalyst B were set forth in Table1.

Example 1

A reaction tube (inner diameter of 20 mm) charged with Catalyst A (100ml) was installed countercurrently in a fixed bed flow type reactor.Thereafter, Catalyst A was pre-sulfurized for 4 hours using astraight-run gas oil (3 mass % sulfur content) containing dimethyldisulfide, under conditions where the catalyst layer average temperaturewas 300° C., the hydrogen partial pressure was 6 MPa, the liquid hourlyspace velocity was 1 h⁻¹, and the hydrogen/oil ratio was 200 NL/L.

After the pre-sulfurization, a hydrotreated oil after being introducedinto a high pressure separator described below was partially recycled tobe incorporated in vegetable fat 1 having properties set forth in Table2 (the ratio of the compound having a triglyceride structure in theoxygen-containing hydrocarbon compound: 98 mol %) so that the amount ofthe hydrotreated oil is one times by mass relative to vegetable fat 1.Dimethyl sulfide was added to the mixture to prepare a feedstock and toadjust the sulfur content (in terms of sulfur) thereof to be 10 ppm bymass. Thereafter, the feedstock was hydrotreated. The feedstock had adensity at 15° C. of 0.900 g/ml and an oxygen content of 11.5 percent bymass. The hydrotreatment was carried out under conditions where thetemperature at the reaction tube inlet was 280° C., the hydrogenpressure was 6.0 MPa, the liquid hourly space velocity was 1.0 h⁻¹, andthe hydrogen/oil ratio was 510 NL/L. A hydrotreated oil produced byhydrotreating the feedstock was introduced into the high pressureseparator to remove hydrogen, hydrogen sulfide, carbon dioxide, andwater. A portion of the hydrotreated oil after being introduced into thehigh pressure separator was cooled to a temperature of 40° C. withcooling water and then recycled to be mixed with the vegetable fat 1 asdescribed above. The hydrotreated oil remaining after recycling wasintroduced into a fixed bed flow type reactor (isomerization unit)equipped with a reaction tube (inner diameter: 20 mm) charged withCatalyst B to be isomerized. Before isomerization, Catalyst B wasreduced for 6 hours under conditions where the catalyst layer averagetemperature was 320° C., the hydrogen pressure was 5 MPa, and thehydrogen gas flow rate was 83 ml/min. Thereafter, isomerization wascarried out under conditions where the catalyst layer averagetemperature was 330° C., the hydrogen pressure was 3 MPa, the liquidhourly space velocity was 1 h⁻¹, and the hydrogen/oil ratio was 500NL/L. The isomerized oil was directed to a rectification tower and thenfractionally distilled into a light fraction having a boiling range oflower than 140° C., a middle fraction of 140 to 280° C., and a heavyfraction of higher than 280° C. The middle fraction was used as anaviation fuel base oil. The hydrotreating conditions and the propertiesof the resulting aviation fuel base oil are set forth in Tables 3 and 4,respectively.

Example 2

Hydrotreatment and isomerization were carried out in the same manner asthat of Example 1 except that the feedstock contained 50 percent byvolume of a petroleum-based base oil having properties set forth inTable 2 and the hydrogen pressure for the hydrotreatment was 3 MPa,thereby producing an aviation fuel base oil. The petroleum-based baseoil to be contained in the feedstock was a straight-run kerosenefraction produced by fractionally distilling a fraction produced bytreating crude oil in an atmospheric distillation unit within a boilingrange of 140 to 270° C. The hydrotreating conditions and the propertiesof the resulting aviation fuel base oil are set forth in Tables 3 and 4,respectively.

Example 3

Hydrotreatment and isomerization were carried out in the same manner asthat of Example 1 except that vegetable fat 1 contained in the feedstockwas changed to vegetable fat 2, and for the hydrotreating, the reactiontube inlet temperature was 360° C., the hydrogen pressure was 10 MPa,and the liquid hourly space velocity was 0.5 h⁻¹. The hydrotreatingconditions and the properties of the resulting aviation fuel base oilare set forth in Tables 3 and 4, respectively.

Example 4

An aviation fuel base oil as set forth in Table 4 was prepared byblending 50 percent by volume of the aviation fuel base oil produced inExample 1 and 50 percent by volume of an aviation fuel base oil havingproperties set forth in Table 2 produced by hydrodesulfurizing afraction fractionated a fraction produced by treating crude oil anatmospheric distillation unit, within a boiling point of 140 to 270° C.

(General Properties of Feedstock and Aviation Fuel Base Oil and AviationFuel)

The general properties of the feedstock and aviation fuel base oil setforth in Tables 2 and 4 refer to values measured by the followingmethods.

The density at 15° C. (density@15° C.) refers to a value measured inaccordance with JIS K2249 “Crude Oil and PetroleumProducts-Determination of density and petroleum measurement tables basedon reference temperature (15° C.)”.

The kinematic viscosity at 30° C. or −20° C. refers to a value measuredin accordance with JIS K2283 “Crude Oil and Petroleum Products-TestMethods for Kinetic Viscosity and Viscosity Index Calculation Method”.

Elemental analysis C (mass %) and H (mass %) refer to values eachdetermined by a method defined by ASTM D 5291 “Standard Test Methods forInstrumental Determination of Carbon, Hydrogen and Nitrogen in PetroleumProducts and Lubricants”.

The oxygen content refers to a value measured by a method such asUOP649-74 “Total Oxygen in Organic Materials by Pyrolysis-GasChromatographic Technique”.

The sulfur content refers to a value measured in accordance with JISK2541 “Crude Oil and Petroleum Products-Determination of sulfurcontent”.

The acid value refers to a value measured in accordance with JIS K2501“Petroleum Products and Lubricating Oils Test Method for NeutralizationNumber”.

The composition ratio of fatty acid groups in animal or vegetable fatrefers to a value determined in accordance with the above-describedStandard Methods for the Analysis of Fats, Oils and Related Materials(established by Japan Oil Chemists' Society) (1993) “2.4.21.3-77 FattyAcid Composition (FID Temperature Programmed Gas Chromatograph Method)”.

The flash point refers to a value determined in accordance with JISK2265 Crude Oil and Petroleum Products-Determination of flash point-TagClosed Cup Method”.

The distillation characteristics refer to values measured in accordancewith JIS K2254 “Petroleum products-Determination of distillationcharacteristics”.

The aromatic content refers to a value measured in accordance with JISK2536 “Liquid petroleum products-Testing method of components(Fluorescent Indicator Adsorption Method)”.

The total acid value refers to a value measured in accordance with JIS2276 “Determination of the Total Acid Value”.

The freezing point refers to a value measured in accordance with JIS2276 “Determination of the freezing point of aviation fuels”.

The smoke point refers to a value measured in accordance with JIS K2537“Petroleum products-Kerosene and aviation turbine fuels-Determination ofsmoke point”.

The thermal stability refers to a value measured in accordance. with JISK2276 “Determination of thermal oxidation stability of gas turbinefuels-JETOT method Method A, Method B”.

(Life Cycle Characteristics)

The life cycle characteristics (life cycle CO₂ calculation) described inthe present Example were calculated by the following method.

Life cycle CO₂ was calculated as the CO₂ generated from oil-welldrilling in the fuel production to pumping to an airplane fuel tank.

The CO₂ generated from oil-well drilling to pumping to an airplane fueltank (hereinafter referred to as “Well to Tank CO₂”) was calculated asthe total CO₂ emissions during a sequence starting from the drilling ofmaterial and crude oil resources, through transportation, processing,and delivery, to pumping to an airplane's fuel tank. For calculation of“Well to Tank CO₂”, the calculation was carried out in consideration ofthe carbon dioxide generated during the following (1B) to (5B) events.Data required for the calculation was the oil refinery operationperformance date possessed by the inventors of the present invention.

(1B) Carbon dioxide emissions accompanied with the use of fuel forvarious processing devices and facilities such as boilers

(2B) Carbon dioxide emissions accompanied with reforming reaction in ahydrogen producing device in a processing using hydrogen

(3B) Carbon dioxide emissions accompanied with regeneration of acatalyst if the processing is carried out through a device such as acatalytic cracking device requiring continuous catalyst regeneration

(4B) Carbon dioxide emissions when a gas oil composition was produced orshipped at Yokohama, Japan, delivered therefrom to Sendai, Japan, andpumped into a vehicle there

(5B) Carbon dioxide emissions when an animal or vegetable fat and acomponent originating therefrom were obtained from Malaysia or regionstherearound, and a gas oil composition was produced in Yokohama, Japan.

As apparent from Table 4, the aviation fuel base oils prepared inaccordance with Examples 1 to 4 using a feedstock originating from ananimal or vegetable fat have excellent properties as aviation fuel baseoils and are novel aviation fuel base oils alternative topetroleum-based fuel, which contribute to the prevention of globalwarming.

TABLE 1 Catalyst A Catalyst B Content Al₂O₃ (mass %, based on supportmass) 91.2 100 Content SiO₂ (mass %, based on support mass) 4.8 0Content P₂O₅ (mass %, based on support mass) 4.0 0 Content MoO₃ (mass %,based on catalyst mass) 24.0 0 Content NiO (mass %, based on catalystmass) 2.6 0 Content Pt (mass %, based on catalyst mass) 0 0.5 PoreVolume (ml/g) 0.75 0.47 Average Pore diameter (nm) 7.0 5.2 Ratio of PoreVolume derived from Pores having 22 39 a pore diameter of 3 nm or lessto Total Pore Volume (% by volume)

TABLE 2 Vagetable Fat 1 Vegetable Fat 2 Petroleum - Aviation Fuel(coconut oil) (palm oil) based Base Oil Base Oil Density at 15° C.(kg/m³) 900 916 792 790 Kinematic viscosity at 30° C. (mm²/s) — — 1.41.3 Elemental Analysis C (mass %) 77.0 77.3 85.2 85.0 H (mass %) 12.012.0 13.3 15.0 Oxygen Content (mass %) 11.5 10.6 <0.1 <0.1 SulfurContent (mass %) <1 <1 1.15 0.05 Acid Value (mgKOH/g) 0.10 0.07 0.000.00 Component Ratio (mass Butyric acid group (C3) 0 0 — — %) of FattyAcid Groups Caproic acid group (C5) 0 0 — — in Fat (number of Caprylicacid group (C7) 4 0 — — carbon atoms in fatty Capric acid group (C9) 4 0— — acid carbon chain) Lauric acid group (C11) 49 0 — — Myristic acidgroup (C13) 17 1 — — Palmitic acid group (C14) 9 44 — — Stearic acidgroup (C16) 3 5 — — Oleic acid group (C17) 7 39 — — Linoleic acid group(C17) 2 10 — — Linolenic acid group (C17) 0 0 — —

TABLE 3 Exam- Exam- Exam- ple 1 ple 2 ple 3 Recycled Amount times bymass 1 1 1 Reaction Temperature ° C. 280 280 360 (Temperature atReaction Tube Inlet) Hydrogen Pressure MPa 6 3 10 LHSV h⁻¹ 1.0 1.0 0.5With or Without Quenching Yes Yes Yes Amount of Addition of ppm by mass10 10 10 Sulfur - Containing Hydrocarbon Compound (to Feedstock)

TABLE 4 Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 Density at 15°C. g/cm³ 0.750 0.771 0.780 0.769 Flash Point ° C. 85 64 75 60Distillation Characteristics T10 ° C. 202.0 185.0 149.5 180.0 T50 ° C.225.0 210.5 168.0 210.0 T90 ° C. 238.0 236.5 254.0 235.5 EP ° C. 258.0259.0 273.5 260.0 Sulfur Cntent mass ppm <1 5 <1 19 Hromatic Content vol% 0 9 0 8 Total Acid Value mgKOH/g 0.00 0.01 0.00 0.01 Freezing Point °C. −47 −45 −40 −45 Smoke Point mm >50 40 35 42 Thermal OxidationStability Filter Pressure kPa 0 0 0 0 Differenc Tube Rating <1 <1 <1 <1Life Cycle g-CO₂/MJ) 40.4 53.8 50.0 54.3 Characteristics (W to W—CO₂emissions)

INDUSTRIAL APPLICABILITY

The present invention provides an environment friendly aviation fuelbase oil having excellent combustibility, oxidation stability andlifecycle properties resulting from its neutral carbon properties andcan contribute to primary energy diversification.

1. A process for producing an aviation fuel base oil comprisinghydrotreating in the presence of hydrogen a feedstock comprising anoxygen-containing hydrocarbon compound originating from an animal orvegetable fat and a sulfur-containing hydrocarbon compound.
 2. Theprocess according to claim 1, wherein said feedstock further comprises apetroleum base oil produced by refining crude oil.
 3. The processaccording to claim 1, wherein the total of the compositions of the fattyacids having a fatty acid hydrocarbon chain of 10 to 14 carbon atoms insaid animal or vegetable fat is 60 percent by mass or more.
 4. Theprocess according to claim 1, wherein said hydrotreating comprises astep wherein said feedstock is hydrotreated in the presence of hydrogenusing a catalyst comprising a porous inorganic oxide comprising two ormore types of elements selected from aluminum, silicon, zirconium,boron, titanium and magnesium and one or more types of metals selectedfrom the group consisting of the Groups 6A and 8 elements of theperiodic table, supported thereon, under conditions where the hydrogenpressure is from 2 to 13 MPa, the liquid hourly space velocity is from0.1 to 3.0 h−1, the hydrogen/oil ratio is from 150 to 1500 NL/L, and thereaction temperature is from 150 to 480° C.
 5. The process according toclaim 4, wherein said hydrotreating comprises a step wherein thehydrotreated oil produced in the said hydrotreating step of claim 4 isfurther isomerized in the presence of hydrogen using a catalystcomprising a porous inorganic oxide comprising two or more types ofelements selected from aluminum, silicon, zirconium, boron, titanium,magnesium and zeolite and one or more types of metals selected from thegroup consisting of the Group 8 elements of the periodic table,supported thereon, under conditions where the hydrogen pressure is from2 to 13 MPa, the liquid hourly space velocity is from 0.1 to 3.0 h−1,the hydrogen/oil ratio is from 250 to 1500 NL/L, and the reactiontemperature is from 150 to 380° C.
 6. A process for producing anaviation fuel base oil wherein the aviation fuel base oil is produced byblending an aviation fuel base oil produced by the process according toclaim 1 and an aviation fuel base oil produced by refining crude oil.